Specifications
In Figure 6, a D1251C sensor module is used to convert
a 0-20mA process signal to ASCII data. The D1251C is
operated in continuous output mode to produce data
without a host. The D1251C will produce an ASCII out-
put data string after every analog-to-digital conversion.
Typical output data shown in Figure 6 is *+00020.00. The
data output is connected to a modem which allows the
data to be transmitted to another modem which may be
located thousands of miles away. The receive modem
reconstructs the ASCII data and feeds it to the D4251
module. The D4251 is configured in continuous input
mode which allows it to accept the data string of
*+00020.00 as an analog output command. The D4251
will respond by producing an output of 20mA.
In this case the process variable sensed by the D1251C
may be accurately reproduced by the D4251 anywhere a
telephone connection is available. The D4251 output will
follow the input signal applied to the D1251C. No host is
necessary on either end to provide a continuous signal.
The continuous input configuration may be used to con-
vert analog data from one type to another. In figure 7, a
thermocouple signal may be converted to a 0-20mA ana-
log output. The D4251 may be rescaled to any input
range, including thermocouple input data. In this case,
we rescale the D4251 to produce a 0-20mA signal corre-
sponding to 100°-300°F at the thermocouple.
Figure 6. Transmitting analog signals over long distances.
Figure 7. Rescaling a temperature input to a 0-20mA output.
Using modems and D3000/4000 modules
The modules can be used with auto-answer modems at
remote sites for long-distance operation. A host computer
may be used to call a modem and check the status of the
process. The modules communicate using RS-232 which
is the standard used by modems to communicate with
devices such as printers or computers.
The modem must be an auto-answer type. When an in-
coming telephone call occurs, the modem will pickup the
telephone line and establish communication with the
computer at the other end. The other modem function re-
quired is the Ignore RS-232C DTR line. The modules do
not support the Data Transmit Ready line so the modem
must ignore it. Since DTR is ignored, the modem and
module are always ready for incoming calls. Other mo-
dem control functions such as: enable auto redial on
busy, enable command mode, etc. are not applicable and
may be set to their default settings.
The computer must have either an internal modem or
ability to connect to an external modem via an RS-232
serial communications port. Terminal software, or
equivalent, is also required to control the modem and
communicate with the remote module.
All communications parameters needed to establish com-
munication with the remote module are shown in the fol-
lowing table.
Terminal Computer Remote D4000
software modem modem module
Baud rate 1200 1200 1200 1200
Parity N N
Data bits 7
Stop bits 1
Auto-dial On
Auto-ans. On
Once configured, have the host computer call the site.
Upon carrier detection from the remote site, begin com-
municating with the remote module. After data gathering
is complete, use the terminal software to hang up the
telephone. Once the telephone is back on the hook, the
remote modem will reset itself and await the next call.
Transmitting analog signals over long distances
The D4000 models may be paired with an appropriate
D1000 module to transmit analog signals over great dis-
tances without a host computer.
D3000/D4000 Ordering Guide
MODEL OUTPUT RANGE/INPUT
Voltage Output
D3121/D4121 ±1V Output/RS-232C Input
D3122/D4122 ±1V Output/RS-485 Input
D3131/D4131 ±5V Output/RS-232C Input
D3132/D4132 ±5V Output/RS-485 Input
D3141/D4141 ±10V Output/RS-232C Input
D3142/D4142 ±10V Output/RS-485 Input
D3161/D4161 0 to 1V Output/RS-232C Input
D3162/D4162 0 to 1V Output/RS-485 Input
MODEL OUTPUT RANGE/INPUT
D3171/D4171 0 to 5V Output/RS-232C Input
D3172/D4172 0 to 5V Output/RS-485 Input
D3181/D4181 0 to 10V Output/RS-232C Input
D3182/D4182 0 to 10V Output/RS-485 Input
Current Output
D3251/D4251 0 to 20mA Output/RS-232C Input
D3252/D4252 0 to 20mA Output/RS-485 Input
D3261/D4261 4 to 20mA Output/RS-232C Input
D3262/D4262 4 to 20mA Output/RS-485 Input